The present invention relates to communications equipment, and more particularly to power saving measures in communications equipment.
In the forthcoming evolution of the mobile cellular communication standards like the Global System for Mobile Communication (GSM) and Wideband Code Division Multiple Access (WCDMA), the focus is very much on high capacity and high throughput to individual users in order to support advanced services like video and multimedia applications. A proposal for such a new flexible cellular system is Super 3G or Long-Term 3G Evolution (henceforth, “LTE”) (the “3G” standing for “third generation”). This proposed new system can be seen as an evolution of the 3G WCDMA standard. LTE is a packet-switched system in which users share a broadband channel. This allows for flexible resource allocation in which a single user can be provided with very high peak rates.
The main track of the LTE standardization process is considering the use of Frequency Division Duplex (FDD) operation, wherein uplink (UL) and downlink (DL) transmission occur on different frequency bands and transmission and reception occur simultaneously. In order to obtain sufficient isolation between transmission and reception, duplexers are needed at the antenna within the terminal (also called “user equipment”—UE—in WCDMA terminology). These duplexers incur extra power losses. Depending on the carrier spacing between UL and DL and the operating frequencies, the duplexer loss varies between 1.5 and 4 dB.
Power consumption has become a real problem for advanced communication systems. One reason is that battery technology cannot keep up with the pace of the increased amount of power required for high data rate services. Moreover, heat dissipation sets new challenges on mobile phone design.
Any losses in the transceiver (TRX) chain have a direct impact on terminal power consumption. Introducing low power modes with low duty cycles is one way to reduce a terminal's power consumption. For example, for voice users, power savings can be achieved by activating the terminal to send and receive a Voice over Internet Protocol (VoIP) packet only during a short window of time that occurs every 20 ms or so. In between these windows, the terminal can save power by entering a low-power sleep mode.
Losses associated with the duplexer can be eliminated by operating the terminal in a half-duplex mode, in which transmission and reception operations are performed during mutually exclusive periods of time. Since, in such operation, the antenna is never used to simultaneously transmit and receive a signal, there is no need for a duplexer in the circuit. For example, such a technique is used in the GSM system, which is an FDD system but which also has a time offset of 3 time slots between UL and DL transmissions.
A problem arises if one wants to reduce power consumption by using both short windows of activity (separated by intervals of operation in a low-power sleep mode) and half-duplex operation. This is because operating in half-duplex mode, by definition, disallows the transmit and receive windows from occurring simultaneously which, in turn, increases the duty cycle.